Given the safety concerns and low energy density induced by liquid electrolytes,the interest in solidstate lithium metal batteries is rapidly growing.Among various solid electrolytes,garnet-type lithium lanthanum zirc...Given the safety concerns and low energy density induced by liquid electrolytes,the interest in solidstate lithium metal batteries is rapidly growing.Among various solid electrolytes,garnet-type lithium lanthanum zirconate (LLZO) has attracted extensive attention due to its numerous advantages.This review systematically summarizes the intrinsic issues faced by unstable bare LLZO and the resolution strategy of metallic doping in the electrochemical application.It comprehensively discusses the doping arrangements for high ionic conductivity based on element types and gap filling using second phases/sintering aids for LLZO grains/pellets.Emphasizing diverse doping strategies for bulk LLZO,it relates to simulation and characterization findings along with novel synthesis approaches.By identifying the inherent scientific questionsof LLZO,this review bridges the long-existing gaps between the doping strategy guidelines for suitable crystalline phase and the surge of high Li^(+)conductivity for practical solid-state lithium batteries.展开更多
The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temper...The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.展开更多
The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced ...The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments.This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines.Based on the first principles,molecular dynamics,and new data-driven calculation approaches,doping and high-entropy strategies have now been adopted in advanced TBC materials design.In this paper,the solid-state heat transfer mechanism of TBCs is explained from two aspects,including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature.This paper also provides new insights into design considerations of adaptive TBC materials,and the challenges and potential breakthroughs are further highlighted for extreme environmental applications.Strategies for improving thermophysical performance are proposed in two approaches:defect engineering and material compositing.展开更多
Based on defect chemistry theory and molecular dynamics,the defect formation energy and its relationship with the mechanism of pyrochlore-fluorite phase change were investigated,so as to reveal the underlying mechanis...Based on defect chemistry theory and molecular dynamics,the defect formation energy and its relationship with the mechanism of pyrochlore-fluorite phase change were investigated,so as to reveal the underlying mechanism of high-temperature stability of pyrochlore zirconates.Results showed that with the rise of the atom mass of A,the defect formation energies decreased that meant the crystal structure tended to become more disordered.Noticeably,the first nearest cation antisite dominated the pyrochlore disorder transformation process.In addition,it was found that the diffusion of oxygen atoms was far higher than that of cations,and was increased with the temperature,thus also promoting the pyrochlore-fluorite transformation process.展开更多
Highly dispersed gadolinium zirconate(GZ)nanoparticles with fluorite structure were successfully synthesized by co-precipitation method,and their phase composition and microstructure,formation mechanism,and grain grow...Highly dispersed gadolinium zirconate(GZ)nanoparticles with fluorite structure were successfully synthesized by co-precipitation method,and their phase composition and microstructure,formation mechanism,and grain growth kinetics were investigated.The results suggest that the nanoparticles were obtained through hydroxide dehydration and solid phase reaction.High dispersion was accomplished by ethanol solvent to reduce the hydrogen bond and sodium dodecyl benzene sulfonate(SDBS)surfactant to increase the electrostatic repulsion between the nanoparticles.The grain growth activation energy of GZ powders calcined at lower temperature(<1200°C)is 86.5 kJ/mol(Ql),and the grain growth activation energy of GZ powders calcined at higher temperature(>1200°C)is 148.4 kJ/mol(Qh).The current study shows that the optimal process to synthesize dispersed GZ nanoparticles includes ethanol solvent,3 wt.%SDBS surfactant,and 1100°C as calcining temperature.展开更多
The effects of the modification of electrode/ceramic interfaces through a chemical solution deposition-derived PbO buffer layer on the fatigue endurance of lead zirconate titanate（PZT） thin films were investigated.T...The effects of the modification of electrode/ceramic interfaces through a chemical solution deposition-derived PbO buffer layer on the fatigue endurance of lead zirconate titanate（PZT） thin films were investigated.The grain size and the surface roughness of the PZT films increased through PbO interfacial modification.Moreover,the PZT films with PbO interfacial modification had a better crystallographic structure and no evident secondary phases were observed.While the remanent polarization and dielectric constant were reduced,the fatigue endurance was improved.Based on the results,the mechanism for the fatigue endurance improvement was discussed.展开更多
The increasing anthropogenic emissions of greenhouse gases(GHG)is encouraging extensive research in CO_(2)utilisation.Dry reforming of methane(DRM)depicts a viable strategy to convert both CO_(2)and CH4into syngas,a w...The increasing anthropogenic emissions of greenhouse gases(GHG)is encouraging extensive research in CO_(2)utilisation.Dry reforming of methane(DRM)depicts a viable strategy to convert both CO_(2)and CH4into syngas,a worthwhile chemical intermediate.Among the different active phases for DRM,the use of nickel as catalyst is economically favourable,but typically deactivates due to sintering and carbon deposition.The stabilisation of Ni at different loadings in cerium zirconate inorganic complex structures is investigated in this work as strategy to develop robust Ni-based DRM catalysts.XRD and TPR-H2analyses confirmed the existence of different phases according to the Ni loading in these materials.Besides,superficial Ni is observed as well as the existence of a CeNiO_(3)perovskite structure.The catalytic activity was tested,proving that 10 wt.%Ni loading is the optimum which maximises conversion.This catalyst was also tested in long-term stability experiments at 600and 800℃in order to study the potential deactivation issues at two different temperatures.At 600℃,carbon formation is the main cause of catalytic deactivation,whereas a robust stability is shown at 800℃,observing no sintering of the active phase evidencing the success of this strategy rendering a new family of economically appealing CO_(2)and biogas mixtures upgrading catalysts.展开更多
Binary fluorozirconate glassZrF_(4)·BaF_(2) has been studied by molecular dynamical simulation using parameter-free Gordon-Kim potentials.In these simulations a novel technique is employed to monitor the motion o...Binary fluorozirconate glassZrF_(4)·BaF_(2) has been studied by molecular dynamical simulation using parameter-free Gordon-Kim potentials.In these simulations a novel technique is employed to monitor the motion of ions,thus the structure pictures of glass and the microscopic motion mechanism of ionic conduction are clearly and directly obtained.The glass networks commonly are formed by ZrF8,ZrF7 or ZrF6 polyhedra,cross linked by Ba-F ionic bonds.The mean distance of the ionic nearest neighboring at 300K is about 3.90Å(Zr-Zr),3.87Å(Zr-Ba),and 1.96Å(Zr-F).The two stronger peaks of five main peaks of vibrational spectra are at about 540-600 and 460-510cm^(-1) and three weaker peaks at about 386-416,322-348,and 183-196cm^(-1).The other properties of glass:density,thermal expansion coefficient,polarization,and glass transition temperature are also examined.展开更多
The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 3...The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current–gate voltage （ID-VG） memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor （LDMOS）. The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.展开更多
Perovskite lead zirconate(PbZrOz)was synthesized in an orthorhombic form at a temperature below the Curie temperature,Tc.The orthorhombic form is a noncentrosymmetric structure which is capable of spontaneous polariza...Perovskite lead zirconate(PbZrOz)was synthesized in an orthorhombic form at a temperature below the Curie temperature,Tc.The orthorhombic form is a noncentrosymmetric structure which is capable of spontaneous polarization.Fourier transform infrared(FTIR)spectra and X-ray diffraction(XRD)patterns confirm the siuccessful synthesis of the lead zirconate;and scanning electron microscopy(SEM)micrographs indicate that PbZrO_(3) particles are moderately dispersed in the natural rubber(NR)matrix.Without an electrical field,the particles merely act as a ferroelectric fller,which can absorb and store additional stress.Under an electrical field,particle induced dipole motents are generated,leading to interparticle interaction and a sub-stantial increase in the storage modulus.At a small amount of lead ziroonate part iculates present in the natural rubber matrix,at a volume fraction of 0.007306,the electrical conductivity increases dramatically by nearly two orders of magnitude at the electrical frequency of 500 kHz.展开更多
Lanthanum-modified lead zirconate titanite （PLZT） piezoelectric ceramics has higher piezoelectric and dielectric properties compared with the common lead zirconate titanite （PZT） ceramics. These properties endue t...Lanthanum-modified lead zirconate titanite （PLZT） piezoelectric ceramics has higher piezoelectric and dielectric properties compared with the common lead zirconate titanite （PZT） ceramics. These properties endue the cymbal hydrophones made of PLZT usually with stable performance but lower receiving sensitivity. In order to improve the sensitivity, through a static analysis on hydrophone we did some changes for the PLZT hydrophone by reducing the radius of the piezoelectric ceramics and sealing its boundary. Furthermore, ANSYS simulations were made, and the experiments for the improved PLZT hydrophone and the original one were carried out in water pool. The results show that the receiving sensitivity of the improved cymbal hydrophone made of PLZT is 3 -4 dB higher than that of the original, and that the frequency response still keeps flat within 18 kHz band.展开更多
In order to describe the characteristics of piezoelectric bimorph, properties of lead zirconate titanate （LZT） film are studied by X-ray diffraction （XRD） and scanning eletron microscope （SEM）. The ratio of PbTi...In order to describe the characteristics of piezoelectric bimorph, properties of lead zirconate titanate （LZT） film are studied by X-ray diffraction （XRD） and scanning eletron microscope （SEM）. The ratio of PbTiOJPbZrO3 in LZT is 53/47, which is around morphotropic phase boundary （MPB）. LZT film is composed of cubic particles with the average size of 5 ~ma. Density of thin film is figured out through the datum measured in experiments. The displacement model used to analyze the driving ability of bimorph is set up, and the effect of elastic intermediate layer is taken into account. Piezoelectric coefficient of LZT film is worked out by using the displacement model. Experiments of driving ability show that deformation of bimorph free end does not increase with times of crystal growth processes and the maximum deformation is obtained after two times crystal growth processes. Finally, the ferroelectric property of the bimorph is investigated and coercive voltage of the bimorph is obtained.展开更多
The high-entropy rare-earth zirconate((La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7),5RE_(2)Zr_(2)O_(7)HEREZs)ceramics were successfully prepared by a new high-speed positive grinding strategy combined with...The high-entropy rare-earth zirconate((La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7),5RE_(2)Zr_(2)O_(7)HEREZs)ceramics were successfully prepared by a new high-speed positive grinding strategy combined with solid-state reaction method.The microstructure,crystal structure,phase composition,and thermophysical and mechanical properties of the samples were systematically investigated through various methods.Results indicate that the samples have a single-phase defect fluorite-type crystal structure with excellent high-temperature thermal stability.The as-prepared samples also demonstrate low thermal conductivity(0.9–1.72 W·m^(−1)·K^(−1)at 273–1273 K)and high coefficient of thermal expansion(CTE,10.9×10^(−6)K^(−1)at 1273 K),as well as outstanding mechanical properties including large Young’s modulus(E=186–257 GPa)and high fracture toughness(KIC).Furthermore,the formation possibility of the as-prepared samples was verified through the first-principles calculations,which suggested the feasibility to form the 5RE_(2)Zr_(2)O_(7)HE-REZs in the thermodynamic direction.Therefore,in view of the excellent multifunctional properties exhibited by the as-prepared 5RE_(2)Zr_(2)O_(7)HE-REZs,they have great potential applications in next-generation thermal-barrier coatings(TBCs).展开更多
Ultrafine-grained(Sm_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7)high-entropy zirconates with single fluorite structure have been fabricated by high-pressure sintering of the self-synthesized nanopowders for ...Ultrafine-grained(Sm_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7)high-entropy zirconates with single fluorite structure have been fabricated by high-pressure sintering of the self-synthesized nanopowders for the first time.The as-sintered samples exhibit a good microstructure with a grain size of 220 nm and a relative density of 96.8%,which yield excellent comprehensive mechanical properties with a high Vickers hardness of 12.5 GPa and a high fracture toughness of 3.4 MPa·m1/2.In addition,the as-sintered samples possess a good thermostability with the grain growth rate of 30 nm/h,and a low thermal conductivity of 1.57 W·m^(-1)·℃^(-1)at room temperature.The superior mechanical and thermal properties are primarily attributed to the“high-entropy”and grain-refinement effects and good interface bonding.展开更多
Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased fo...Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased for enhancing its in-service life.As the Gd element plays an important role in the CMAS resistance,three GZ coatings (GZ-0.75,GZ-1.0,and GZ-1.2) with different Gd/Zr atomic ratios are designed and deposited by laser enhanced chemical vapor deposition(LCVD) in this work.It is found that the generated Gd-apatite in GZ-1.2 would block micro-cracks inside the column structure and the inter-columnar gap more efficiently.Thus,the CMAS penetration rate (5.2 μm/h) of GZ-1.2 decreases over 27% comparing with GZ-1.0 and GZ-0.75,which is even lower than the Gd_(2)Zr_(2)O_(7) coatings fabricated by electron-beam physical vapor depositions (EB-PVDs).This work provides a feasible way to adjust the coating's corrosion resistance and may guide the development of future coating for long in-service life.展开更多
The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyac...The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyacrylamide gel method.In this work,single-phase high-entropy(Lao.2Ndo.2Smo.2Gdo.2 Ybo.2)2Zr2O7 and(Lao.2Ndo.2Yo.2Euo.2Gdo.2)2Zr2O7 nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time.The results showed that phase composition,particle size,and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide(AM)/Zr and calcination temperature.These as-synthesized high-entropy zirconate(HEZ)nanopowders could be sintered into fully dense ceramics at 1500 C for 2 h.These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature.Additionally,two-step sintering of these nanopowders was conducted,and the HEZ ceramics with fine grains were prepared.The polyacrylamide gel method is simple and easily operated,which is a facile approach of producing the HEC nanopowders with excellent sinterability.展开更多
The high-purity and superfine high-entropy zirconate nanopowders,namely(Y_(0.25)La_(0.25)Sm_(0.25)Eu_(0.25))_(2)Zr_(2)O_(7)nanopowders,without agglomeration,were successfully synthesized via polymerized complex method...The high-purity and superfine high-entropy zirconate nanopowders,namely(Y_(0.25)La_(0.25)Sm_(0.25)Eu_(0.25))_(2)Zr_(2)O_(7)nanopowders,without agglomeration,were successfully synthesized via polymerized complex method at low temperatures for the first time.The results showed that the crystallinity degree,lattice strain,and particle size of the as-synthesized powders were gradually enhanced with the increase of the synthesis temperature from 800 to 1300℃.The as-synthesized powders involved fluorite phase in the range of 800-1200℃while they underwent the phase evolution from fluorite to pyrochlore at 1300℃.It is worth mentioning that the as-synthesized powders at 900℃are of the highest quality among all the as-synthesized powders,which is due to the fact that they not only possess the particle size of 11 nm without agglomeration,but also show high purity and good compositional uniformity.展开更多
Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forc...Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coating applications.展开更多
To better understand the generation of electric power for piezoelectric Pb Zr Ti O3(PZT)ceramic plate(?25 mm),an attempt was made to investigate experimentally and numerically electricpower generation characteristics ...To better understand the generation of electric power for piezoelectric Pb Zr Ti O3(PZT)ceramic plate(?25 mm),an attempt was made to investigate experimentally and numerically electricpower generation characteristics during cyclic bending under various loading fixtures(?0–?20 mm),i.e.,different contact areas.Increasing the load-contact area on the PZT ceramic leads to a nonlinear decrease in the generated voltage.Decreasing contact area basically enhances the generated voltage,although the voltage saturates during loading when the contact area is less than?5 mm.A similar voltage is generated for?0 and?5 mm,which is attributed to strain status(ratio of compressive and tensile strain)and material failure due to different stress distribution in the PZT ceramic.On the basis of the obtained electric generation voltage,suitable loading conditions are clarified by loading with the?5 mm fixture,which generates a higher voltage and a longer lifetime of the PZT ceramic.From this approach,it is appeared that the area contact with the area ratio of 0.04(?5 mm/?20 mm)is suitable to obtain the high efficiency of the electric voltage.展开更多
The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with t...The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-temperature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L0 and the expansion coefficient (dL/L0)/dT can reach 2.展开更多
基金supported by the National Natural Science Foundation of China(No.52303245)the Innovative Training/Entrepreneurial Program for Undergraduate(No.202410057057)the"Huacai"training special program of Tianjin University of Science and Technology
文摘Given the safety concerns and low energy density induced by liquid electrolytes,the interest in solidstate lithium metal batteries is rapidly growing.Among various solid electrolytes,garnet-type lithium lanthanum zirconate (LLZO) has attracted extensive attention due to its numerous advantages.This review systematically summarizes the intrinsic issues faced by unstable bare LLZO and the resolution strategy of metallic doping in the electrochemical application.It comprehensively discusses the doping arrangements for high ionic conductivity based on element types and gap filling using second phases/sintering aids for LLZO grains/pellets.Emphasizing diverse doping strategies for bulk LLZO,it relates to simulation and characterization findings along with novel synthesis approaches.By identifying the inherent scientific questionsof LLZO,this review bridges the long-existing gaps between the doping strategy guidelines for suitable crystalline phase and the surge of high Li^(+)conductivity for practical solid-state lithium batteries.
基金supported by the Postdoctoral Foundation of China (20060400261)the Special Finance Scheme of Post Doctoral Foundation of China (200801350)
文摘The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.
基金the financial support from the National Natural Science Foundation of China(Nos.51572061,51621091,and 51321061)the Heilongjiang Touyan Team Program。
文摘The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments.This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines.Based on the first principles,molecular dynamics,and new data-driven calculation approaches,doping and high-entropy strategies have now been adopted in advanced TBC materials design.In this paper,the solid-state heat transfer mechanism of TBCs is explained from two aspects,including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature.This paper also provides new insights into design considerations of adaptive TBC materials,and the challenges and potential breakthroughs are further highlighted for extreme environmental applications.Strategies for improving thermophysical performance are proposed in two approaches:defect engineering and material compositing.
基金Sponsored by the National Natural Science Foundation of China (50801005)
文摘Based on defect chemistry theory and molecular dynamics,the defect formation energy and its relationship with the mechanism of pyrochlore-fluorite phase change were investigated,so as to reveal the underlying mechanism of high-temperature stability of pyrochlore zirconates.Results showed that with the rise of the atom mass of A,the defect formation energies decreased that meant the crystal structure tended to become more disordered.Noticeably,the first nearest cation antisite dominated the pyrochlore disorder transformation process.In addition,it was found that the diffusion of oxygen atoms was far higher than that of cations,and was increased with the temperature,thus also promoting the pyrochlore-fluorite transformation process.
基金This study was supported by the National Key Research and Development Program of China(grant 2017YFB0306100)the Natural Science Foundation of Hunan Province(grant 2018JJ2524)the International scientific technological cooperation projects of China(grants 2015DFR50580 and 2013DFA31440).
文摘Highly dispersed gadolinium zirconate(GZ)nanoparticles with fluorite structure were successfully synthesized by co-precipitation method,and their phase composition and microstructure,formation mechanism,and grain growth kinetics were investigated.The results suggest that the nanoparticles were obtained through hydroxide dehydration and solid phase reaction.High dispersion was accomplished by ethanol solvent to reduce the hydrogen bond and sodium dodecyl benzene sulfonate(SDBS)surfactant to increase the electrostatic repulsion between the nanoparticles.The grain growth activation energy of GZ powders calcined at lower temperature(<1200°C)is 86.5 kJ/mol(Ql),and the grain growth activation energy of GZ powders calcined at higher temperature(>1200°C)is 148.4 kJ/mol(Qh).The current study shows that the optimal process to synthesize dispersed GZ nanoparticles includes ethanol solvent,3 wt.%SDBS surfactant,and 1100°C as calcining temperature.
基金support of Beijing Nova Program of China (2007B025)the National Natural Science Foundation of China (10979013)+1 种基金the Innovative Research Team in Universities (IRT 0509)the Major State Basic Research Development Program of China (No.2009CB623306)
文摘The effects of the modification of electrode/ceramic interfaces through a chemical solution deposition-derived PbO buffer layer on the fatigue endurance of lead zirconate titanate（PZT） thin films were investigated.The grain size and the surface roughness of the PZT films increased through PbO interfacial modification.Moreover,the PZT films with PbO interfacial modification had a better crystallographic structure and no evident secondary phases were observed.While the remanent polarization and dielectric constant were reduced,the fatigue endurance was improved.Based on the results,the mechanism for the fatigue endurance improvement was discussed.
基金supported by grant PID2019-108502RJ-I00 and grant IJC2019-040560-I both funded by MCIN/AEI/10.13039/501100011033RYC2018-024387-I funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future。
文摘The increasing anthropogenic emissions of greenhouse gases(GHG)is encouraging extensive research in CO_(2)utilisation.Dry reforming of methane(DRM)depicts a viable strategy to convert both CO_(2)and CH4into syngas,a worthwhile chemical intermediate.Among the different active phases for DRM,the use of nickel as catalyst is economically favourable,but typically deactivates due to sintering and carbon deposition.The stabilisation of Ni at different loadings in cerium zirconate inorganic complex structures is investigated in this work as strategy to develop robust Ni-based DRM catalysts.XRD and TPR-H2analyses confirmed the existence of different phases according to the Ni loading in these materials.Besides,superficial Ni is observed as well as the existence of a CeNiO_(3)perovskite structure.The catalytic activity was tested,proving that 10 wt.%Ni loading is the optimum which maximises conversion.This catalyst was also tested in long-term stability experiments at 600and 800℃in order to study the potential deactivation issues at two different temperatures.At 600℃,carbon formation is the main cause of catalytic deactivation,whereas a robust stability is shown at 800℃,observing no sintering of the active phase evidencing the success of this strategy rendering a new family of economically appealing CO_(2)and biogas mixtures upgrading catalysts.
基金Supported by the U.S.Army Research Office under Grant No.DAAL-03-92-G-0366the National Natural Science Foundation of China(NSFC)-the Subproject of the Major Project of NSFC:Theoretical Chemistry of Solid Suface and Its Application。
文摘Binary fluorozirconate glassZrF_(4)·BaF_(2) has been studied by molecular dynamical simulation using parameter-free Gordon-Kim potentials.In these simulations a novel technique is employed to monitor the motion of ions,thus the structure pictures of glass and the microscopic motion mechanism of ionic conduction are clearly and directly obtained.The glass networks commonly are formed by ZrF8,ZrF7 or ZrF6 polyhedra,cross linked by Ba-F ionic bonds.The mean distance of the ionic nearest neighboring at 300K is about 3.90Å(Zr-Zr),3.87Å(Zr-Ba),and 1.96Å(Zr-F).The two stronger peaks of five main peaks of vibrational spectra are at about 540-600 and 460-510cm^(-1) and three weaker peaks at about 386-416,322-348,and 183-196cm^(-1).The other properties of glass:density,thermal expansion coefficient,polarization,and glass transition temperature are also examined.
基金the National Basic Research Program of China(Grant No.50772019)the National Natural Science Foundation of China(Grant No.61204084)
文摘The behaviors of lead zirconate titanate （PZT） deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current–gate voltage （ID-VG） memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor （LDMOS）. The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.
文摘Perovskite lead zirconate(PbZrOz)was synthesized in an orthorhombic form at a temperature below the Curie temperature,Tc.The orthorhombic form is a noncentrosymmetric structure which is capable of spontaneous polarization.Fourier transform infrared(FTIR)spectra and X-ray diffraction(XRD)patterns confirm the siuccessful synthesis of the lead zirconate;and scanning electron microscopy(SEM)micrographs indicate that PbZrO_(3) particles are moderately dispersed in the natural rubber(NR)matrix.Without an electrical field,the particles merely act as a ferroelectric fller,which can absorb and store additional stress.Under an electrical field,particle induced dipole motents are generated,leading to interparticle interaction and a sub-stantial increase in the storage modulus.At a small amount of lead ziroonate part iculates present in the natural rubber matrix,at a volume fraction of 0.007306,the electrical conductivity increases dramatically by nearly two orders of magnitude at the electrical frequency of 500 kHz.
文摘Lanthanum-modified lead zirconate titanite （PLZT） piezoelectric ceramics has higher piezoelectric and dielectric properties compared with the common lead zirconate titanite （PZT） ceramics. These properties endue the cymbal hydrophones made of PLZT usually with stable performance but lower receiving sensitivity. In order to improve the sensitivity, through a static analysis on hydrophone we did some changes for the PLZT hydrophone by reducing the radius of the piezoelectric ceramics and sealing its boundary. Furthermore, ANSYS simulations were made, and the experiments for the improved PLZT hydrophone and the original one were carried out in water pool. The results show that the receiving sensitivity of the improved cymbal hydrophone made of PLZT is 3 -4 dB higher than that of the original, and that the frequency response still keeps flat within 18 kHz band.
基金This project is supported by National Natural Science Foundation of China (No.50675025)Scientific Research Foundation of Ministry of Education,Dalian City for the Returned Overseas Chinese ScholarsDoctoral Startup Fund of Liaoning Province of China (No.20051080).
文摘In order to describe the characteristics of piezoelectric bimorph, properties of lead zirconate titanate （LZT） film are studied by X-ray diffraction （XRD） and scanning eletron microscope （SEM）. The ratio of PbTiOJPbZrO3 in LZT is 53/47, which is around morphotropic phase boundary （MPB）. LZT film is composed of cubic particles with the average size of 5 ~ma. Density of thin film is figured out through the datum measured in experiments. The displacement model used to analyze the driving ability of bimorph is set up, and the effect of elastic intermediate layer is taken into account. Piezoelectric coefficient of LZT film is worked out by using the displacement model. Experiments of driving ability show that deformation of bimorph free end does not increase with times of crystal growth processes and the maximum deformation is obtained after two times crystal growth processes. Finally, the ferroelectric property of the bimorph is investigated and coercive voltage of the bimorph is obtained.
基金This work is supported by the National Science and Technology Major Project(2017-VI-0020-0093)the National Natural Science Foundation of China(12090031).
文摘The high-entropy rare-earth zirconate((La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7),5RE_(2)Zr_(2)O_(7)HEREZs)ceramics were successfully prepared by a new high-speed positive grinding strategy combined with solid-state reaction method.The microstructure,crystal structure,phase composition,and thermophysical and mechanical properties of the samples were systematically investigated through various methods.Results indicate that the samples have a single-phase defect fluorite-type crystal structure with excellent high-temperature thermal stability.The as-prepared samples also demonstrate low thermal conductivity(0.9–1.72 W·m^(−1)·K^(−1)at 273–1273 K)and high coefficient of thermal expansion(CTE,10.9×10^(−6)K^(−1)at 1273 K),as well as outstanding mechanical properties including large Young’s modulus(E=186–257 GPa)and high fracture toughness(KIC).Furthermore,the formation possibility of the as-prepared samples was verified through the first-principles calculations,which suggested the feasibility to form the 5RE_(2)Zr_(2)O_(7)HE-REZs in the thermodynamic direction.Therefore,in view of the excellent multifunctional properties exhibited by the as-prepared 5RE_(2)Zr_(2)O_(7)HE-REZs,they have great potential applications in next-generation thermal-barrier coatings(TBCs).
基金support from the National Key Research and Development Program of China(No.2021YFA0715801)the National Natural Science Foundation of China(No.51972116 and 52122204)+1 种基金the,Guangzhou Basic and Applied Basic Research Foundation(No.202201010632)the China Postdoctoral Science Foundation(2021M691051).
文摘Ultrafine-grained(Sm_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7)high-entropy zirconates with single fluorite structure have been fabricated by high-pressure sintering of the self-synthesized nanopowders for the first time.The as-sintered samples exhibit a good microstructure with a grain size of 220 nm and a relative density of 96.8%,which yield excellent comprehensive mechanical properties with a high Vickers hardness of 12.5 GPa and a high fracture toughness of 3.4 MPa·m1/2.In addition,the as-sintered samples possess a good thermostability with the grain growth rate of 30 nm/h,and a low thermal conductivity of 1.57 W·m^(-1)·℃^(-1)at room temperature.The superior mechanical and thermal properties are primarily attributed to the“high-entropy”and grain-refinement effects and good interface bonding.
基金This work was supported by the Natural Science Foundation of Shanghai(No.20ZR1419200)National Natural Science Foundation of China(Nos.52072232 and 52072231)the Program for Professor of Special Appointment(Eastern Scholar)by Shanghai Municipal Education Commission(No.TP2015040).
文摘Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased for enhancing its in-service life.As the Gd element plays an important role in the CMAS resistance,three GZ coatings (GZ-0.75,GZ-1.0,and GZ-1.2) with different Gd/Zr atomic ratios are designed and deposited by laser enhanced chemical vapor deposition(LCVD) in this work.It is found that the generated Gd-apatite in GZ-1.2 would block micro-cracks inside the column structure and the inter-columnar gap more efficiently.Thus,the CMAS penetration rate (5.2 μm/h) of GZ-1.2 decreases over 27% comparing with GZ-1.0 and GZ-0.75,which is even lower than the Gd_(2)Zr_(2)O_(7) coatings fabricated by electron-beam physical vapor depositions (EB-PVDs).This work provides a feasible way to adjust the coating's corrosion resistance and may guide the development of future coating for long in-service life.
基金supported by the Key Research and Development Projects of Shaanxi Province(Grant No.2021GY-250)the Open Project of State Key Laboratory of Environment-Friendly Energy Materials(Grant No.20kfhg06)the Fundamental Research Funds for the Central Universities of China(Grant No.300102312406).
文摘The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyacrylamide gel method.In this work,single-phase high-entropy(Lao.2Ndo.2Smo.2Gdo.2 Ybo.2)2Zr2O7 and(Lao.2Ndo.2Yo.2Euo.2Gdo.2)2Zr2O7 nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time.The results showed that phase composition,particle size,and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide(AM)/Zr and calcination temperature.These as-synthesized high-entropy zirconate(HEZ)nanopowders could be sintered into fully dense ceramics at 1500 C for 2 h.These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature.Additionally,two-step sintering of these nanopowders was conducted,and the HEZ ceramics with fine grains were prepared.The polyacrylamide gel method is simple and easily operated,which is a facile approach of producing the HEC nanopowders with excellent sinterability.
基金support from the National Natural Science Foundation of China(Nos.52122204 and 51972116)the Guangdong Basic and Applied Basic Research Foundation(Nos.2019A1515012145 and 2021A1515010603)+1 种基金the Fundamental Research Foundation for the Central Universities(No.2020ZYGXZR080)the Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory(No.JCKYS2020607003).
文摘The high-purity and superfine high-entropy zirconate nanopowders,namely(Y_(0.25)La_(0.25)Sm_(0.25)Eu_(0.25))_(2)Zr_(2)O_(7)nanopowders,without agglomeration,were successfully synthesized via polymerized complex method at low temperatures for the first time.The results showed that the crystallinity degree,lattice strain,and particle size of the as-synthesized powders were gradually enhanced with the increase of the synthesis temperature from 800 to 1300℃.The as-synthesized powders involved fluorite phase in the range of 800-1200℃while they underwent the phase evolution from fluorite to pyrochlore at 1300℃.It is worth mentioning that the as-synthesized powders at 900℃are of the highest quality among all the as-synthesized powders,which is due to the fact that they not only possess the particle size of 11 nm without agglomeration,but also show high purity and good compositional uniformity.
基金This work is supported by the National Natural Science Foundation of China(Nos.51865044,52062040)Science and Technology Projects of Inner Mongolia Autonomous Region(Nos.2021PT0008,2022ZD02,2022MS05003)Basic Scientific Research Expenses Program of Universities Directly under Inner Mongolia Autonomous Region(Nos.JY20220041,JY20220062).
文摘Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coating applications.
文摘To better understand the generation of electric power for piezoelectric Pb Zr Ti O3(PZT)ceramic plate(?25 mm),an attempt was made to investigate experimentally and numerically electricpower generation characteristics during cyclic bending under various loading fixtures(?0–?20 mm),i.e.,different contact areas.Increasing the load-contact area on the PZT ceramic leads to a nonlinear decrease in the generated voltage.Decreasing contact area basically enhances the generated voltage,although the voltage saturates during loading when the contact area is less than?5 mm.A similar voltage is generated for?0 and?5 mm,which is attributed to strain status(ratio of compressive and tensile strain)and material failure due to different stress distribution in the PZT ceramic.On the basis of the obtained electric generation voltage,suitable loading conditions are clarified by loading with the?5 mm fixture,which generates a higher voltage and a longer lifetime of the PZT ceramic.From this approach,it is appeared that the area contact with the area ratio of 0.04(?5 mm/?20 mm)is suitable to obtain the high efficiency of the electric voltage.
基金This work was supported by the National Defensive Pre-research Fund of China (Grant No. 98J2.1.9).
文摘The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-temperature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L0 and the expansion coefficient (dL/L0)/dT can reach 2.
